1. Field of the Invention
The present invention pertains to well completion apparatus and methods used in connection with oil wells, gas wells, and the like. Well completion operations are typically performed after the drilling of a well is complete to prepare the well for production. The well is usually cased and a liner may be installed within the casing near the lower end thereof. The production tubing is typically installed within and/or extending upwardly from the liner. It is then necessary to provide for sealing between the outer surface of the tubing and the inner surface of the casing.
2. Description of the Prior Art
One method of providing such a seal is to install a suitable sleeve in the casing above the upper end of the liner and seal between the sleeve and the casing with a permanent packer. The tubing is then allowed to extend into the sleeve and another seal is provided between the tubing and the sleeve. The main problem with this arrangement is the relative permanence of the installation which makes workover operations and the like difficult and expensive.
Another approach is to allow the tubing to extend into the liner or an extension thereof and provide a seal therebetween. Then, if the liner is sealed with respect to the casing by cement and/or a packer, the tubing is effectively sealed with respect to the casing. This arrangement is generally acceptable if a relatively large diameter tubing is employed, i.e. one whose diameter is comparable to the diameter of the liner. However, problems may arise when relatively small diameter tubing is employed and pressure builds up in the area below the seal. This is because a large annular cross-sectional area defined by the inner diameters of the tubing and liner is available to act as a piston in resisting the pressure and tending to urge the tubing string upwardly. This in turn can cause deformation and damage to the tubing.